There are a wide variety of applications that use spark erosion or electrical discharge machining (EDM) for high precision machining of a wide variety of conductive metals. The EDM process removes metal from a metal workpiece by using thermal energy produced from an accurately controlled electrical discharge spark to erode or vaporize metals. One type of electrical discharge machining is known as a die-sinking process in which the inverted image of a metal burning electrode is gradually impressed into the workpiece. The position of the electrode is typically driven and accurately controlled by a servo actuated ram. During an EDM process, the spark discharge is pulsed on and off at a high frequency cycle. Each spark discharge melts or vaporizes a small area of the workpiece surface. The melted metal particles are then cooled by the dielectric fluid in which the work piece is immersed in and then solidified into small erodable particles which are flushed away by the pressure and flow of the dielectric fluid. The impression of the electrode for each spark discharge is located in a very small area. The spark discharge typically travels the shortest distance across the narrowest gap through the dielectric fluid to the closest point on the workpiece thereby removing material at that location. The amount of material removed from the workpiece with each pulse is proportional to the energy contained in the pulse.
The advantages of EDM are well known, including the ability to remove material from workpieces that are very hard such as hardened steel or tungsten carbide with metal burning electrodes formed of soft conductive material such as copper with a tellurium pattern, or graphite. The EDM process is also highly precise and able to easily form complex patterns on a workpiece.
To interchangeably mount a variety of die-sinking electrodes on the ram, electrode holders and mounts are often used to releasably connect the electrodes to the ram. The electrode holder connects on the end of a ram. The mount is interposed between the electrode holder and the electrode. The mount typically includes a shank portion that is clamped into an opening of the electrode holder and a connector portion or tip portion which connects to the electrode.
As shown and described in a General Catalogue published by EROWA (1997), pages 78-100, a variety of mounts have been forged and/or machined from relatively hard conductive material including brass and steel material. A common way to connect a mount to the electrode is to machine threads on the tip portion of the mount which in turn screws into a tapped threaded hole formed in the electrode. It is also known to glue the mount directly on the electrode. For example, it is known to glue a closely machined smooth or slightly roughened cylindrical tip of the mount into a closely machined cylindrical hole in the electrode. It is a requirement that the mount be in good electrical contact with the electrode to facilitate communication of electricity therethrough for proper spark erosion of a work piece. The glue tends to act as an insulator and can cause problems in the EDM process when bad electrical contact exists. Therefore, close tolerances in the machining of the mounts has been necessary to ensure good electrical contact between the mount and the electrode. Even with closely machined tolerances, the glue can still occasionally cause poor electrical contact which is a significant disadvantage. Heretofore, prior mounts for interposition between an electrode holder and an electrode have suffered from being very expensive.